Organic light-emitting diodes, which have long been known, use the electroluminescence of certain organic compounds. An OLED's structure and the tasks of its individual layers are exemplified in FIG. 1:
A layer sequence of organic substances is arranged between two electrodes, of which at least one must be translucent, each organic substance having a specific function within the device.    1. The cathode consists of a base metal or an alloy (e.g. aluminium or calcium) and has the function of injecting electrons;    2. The buffer layer consists of certain metal salts or the oxides thereof, e.g. LiF, and has the function of improving the electron injection into the layer 3;    3. The electron conductor can e.g. consist of Alq3 (tris-(8-hydroxychinolinato)-aluminium) and conducts the electrons from the cathode to the emitting layer or the hole conductor inside the device;    4. The hole conductor mainly consists of triphenylamine derivatives; several hole conductor layers can be provided whose characteristics are adapted to the device and whose function is to transport the holes to the emitting layer;    5. The anode consists of ITO which injects the holes into the hole transport layer;    6. The substrate consists of a transparent material, e.g. glass.
An arrangement of the type described above emits green light generated due to the excitation of Alq3 by the excitons formed from the holes and electrons.
However, such a simple arrangement has several drawbacks:    1. Alq3 only emits light in the green spectral range;    2. The emission band of Alq3 is too broad.
Said drawbacks can in part be eliminated by doping. This means that one or more substances are co-evaporated during the diode's production process. In general, these substances are contained in the Alq3 layer in an amount ranging up to a few percent. Said co-evaporation process is difficult to control.